<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>$root</title>
  <script src="../../js/vue.js"></script>
</head>

<body>
  <div id="app">
    <root-component/>
  </div>

  <script>
    let rootComponent = {
      template: `
        <div>
          $root.msg: {{ $root.msg }}
          <br>
          <button @click="$root.msg ='酒神咒'">改变 msg</button>
        </div>`,
    }

    let vm = new Vue({
      el: '#app',
      data() {
        return {
          msg: '万剑诀'
        }
      },
      components: {
        rootComponent
      },
      methods: {
        handle () {
          console.log(this.msg)
        }
      }
    });
    console.log(vm);
  </script>
</body>

</html>